I. Field of the Invention
The present invention relates to communication systems in general, and to power control in a communication system in particular.
II. Description of the Related Art
There are many in prior art communications systems that require a measurement of the strength of a signal received by a mobile station. For example, during handoff of a mobile station from one base station to another a determination of the strength of the signals received by the mobile station is desirable for determining when to perform the handoff. One such handoff technique is disclosed in U.S. Pat. No. 5,267,261, entitled “MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM,” assigned to the assignee of the present invention.
In the improved technique of U.S. Pat. No. 5,267,261 the mobile station monitors the signal strength of pilot signals transmitted by neighboring base stations within the system. The mobile station sends a signal strength message to a system controller via the base station through which the mobile station is communicating. Command messages from the system controller to a new base station and to the mobile station in response to the signal strength are thus used to establish communication through the new and current base stations. The mobile station detects when the signal strength of a pilot signal corresponding to at least one of the base stations through which the mobile unit is currently communicating has fallen below a predetermined level. The mobile station reports the measured signal strength indicative of the corresponding base station to the system controller via the base stations through which it is communicating. Command messages from the system controller to the identified base station and mobile station terminate communication through the corresponding base station while communications through the other base station or stations continue.
It is known for the power control information transmitted from the mobile station to be inserted into a dedicated control channel separate from the traffic channel. However, it is desirable to decrease the need for separate control channels. Additionally, while it is preferable for the power of the energy of the signal sent on the traffic channel to be used to determine the power control parameters, it is known, for the control information to be based upon the error rate rather than the signal-to-noise ratio because the signal-to-noise ratio of the traffic channel is difficult to measure. For example, in some current systems, the time between errors is used to indicate the error rate. The error rate is then used to determine the quality of the traffic channel. Furthermore, it is difficult to obtain power control information and utilize it in time to respond to the conditions indicated in the power control information.